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11.
Iain Moore Matteo Ceriotti 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2021,67(9):3027-3044
A major cause of spacecraft orbital variation comes from natural perturbations, which, in close proximity of a body, are dominated by its non-spherical nature. For small bodies, such as asteroids, these effects can be considerable, given their uneven (and uncertain) mass distribution. Solar sail technology is proposed to reduce or eliminate the net secular effects of the irregular gravity field on the orbit. Initially, a sensitivity analysis will be carried out on the system which will show high sensitivity to changes in initial conditions. This presents a challenge for optimisation methods which require an initial guess of the solution. As such, the Genetic Algorithm (GA) is proposed as the preferred optimisation method as this requires no initial guess from the user. A multi-objective optimisation is performed which aims to achieve a periodic orbit whilst also minimising the effort required by the sail to do so. Given the system sensitivity, the control law for one orbit is not necessarily applicable for any subsequent orbit. Therefore, a new method of updating the control law for subsequent orbits is presented, based on linearisation and use of a Control Transition Matrix (CTM). The techniques will later find application in a multiple asteroid rendezvous mission with a solar sail as the primary propulsion system. 相似文献
12.
《中国航空学报》2021,34(4):253-264
In the 3D free bending forming system, the bending die can be designed either in a sliding type or rolling friction type. Bending die-based sliding friction type is often called normal bending dies; however, the bending dies-based rolling friction type includes bending die-based roller type and ball type in structure. In the current study, the impact of three bending dies on the forming force, and the bent tube quality was investigated. The obtained results showed that the tangential stresses and strains of the tubes formed by the bending die-based roller type were the smallest among the three bending dies. Besides, the spherical bearing force PU was reduced drastically after using the roller type and ball type compared to the sliding friction type. Moreover, the uniformity of the wall thickness distribution of the tubes formed by the roller type and ball type was better than those obtained from the sliding friction type. In addition, the cross-section distortion rate was reduced by 2.8% using the roller type, and 1.8% using ball-type compared to the sliding friction type. 相似文献
13.
基于空间解析几何理论及运动学分析方法,建立复合材料球形压力容器平面缠绕落纱点轨迹运动方程,推导出等极孔球形容器表面缠绕纤维落纱点空间位置、速度以及加速度的求解函数;通过对落纱点运动规律的分析,解出空间落纱点各方向运动速度的大小及其各方向夹角余弦值。最后利用Matlab软件对不同的丝嘴运动平面倾斜角的缠绕轨迹进行模拟,通过该计算方法模拟的轨迹结果与实际球形容器缠绕线型相符合,验证了该算法的有效性。 相似文献
14.
光致伸缩作动器对开口球壳的主动振动控制 总被引:2,自引:1,他引:1
基于电压源模型,推导出薄膜式光致伸缩作动器应变与光强的本构关系。建立光电层合球壳系统动力学方程及模态控制方程。利用规格化后的模态控制因子对球壳子午线方向及圆周方向的薄膜与弯矩效应进行评价,不同位置下的模态控制因子为作动器布局优化提供了依据。将LQR控制算法与光源激励策略相结合,确定光电层合球壳系统的主动控制策略。进行主动振动控制仿真,得到球壳位移及控制光强响应曲线。仿真结果表明,在较低能量的控制光强下,光致伸缩作动器可实现对球壳的主动振动控制,且振动抑制效果明显。
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15.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(6):2759-2769
In this study, predictions of the E-CHAIM ionospheric model are compared with measurements by the incoherent scatter radars RISR at Resolute Bay, Canada, in the northern polar cap. Reasonable coverage was available for all seasons except winter for which no conclusions were drawn. It is shown that ratios of the model-to measured electron densities are close to unity in the central part of the F layer, around its peak. This is particularly evident for summer daytime. Distributions of the ratios are wider for other seasons indicating larger number of cases when the model underestimates or overestimates. E-CHAIM underestimates the electron density at ionospheric topside and bottomside by ~ 10–20 %. At the bottomside, the underestimations are strongest in summer and equinoctial nighttime. At the topside, the underestimations are strongest in autumn nighttime. Model overestimations are noticeable in the middle part of the F layer during dawn hours in autumn. Overall, the model tends to not predict highest-observed peak electron densities and the largest-observed heights of the peak. 相似文献
16.
Qiumin Dai Xiande Fang Yu Xu 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2013
Forced convective heat transfer is one of the major factors that dominate the thermal behaviors of aerostats. Due to the large physical size, the convection around an aerostat has high Reynolds numbers. The existing forced convective heat transfer correlations are limited to the Reynolds number lower than 105, which are not appropriate for aerostat applications. Therefore, it is necessary to obtain a convective heat transfer correlation applicable to spherical aerostats at high Reynolds numbers. In this paper, steady convective heat transfer from an isothermal spherical aerostat is numerically investigated. The numerical simulation is carried out by commercial computational fluid dynamic software with the Reynolds number from 20 to 108. The average Nusselt numbers are obtained and compared with those of available in literature. Based on regression and optimization with software, a new piecewise correlation of Nusselt number is proposed. The verification shows that the new correlation is reliable. 相似文献
17.
18.
ZN—3探空火箭头罩分离的分析及弹射分离器的设计 总被引:2,自引:0,他引:2
本文应用结构动力学原理,对ZN-3探空火箭头罩铰链式分离及其分离机构进行研究,并用铝合金和玻璃钢两种头罩得出了地面试验的结果,从而获得一些有用的结论。 相似文献
19.
对运载火箭挡火帽可靠性进行了深入的分析,评估,对挡火帽材料的失效机理作了较为深入的探讨,在此基础上进行了可靠性试验及可靠性仿真计算,提出了挡火帽可靠生增长的措施。 相似文献
20.
介绍了用于制造单分散球形微米级粒子的脉冲微孔喷射技术.根据微滴制备原理,可将其分为适用于低熔点材料的压片式喷射装置及适用于高熔点材料的传动杆式喷射装置,分别阐述了两种方式的脉冲微孔喷射技术的喷射原理、相关特点以及该技术的发展和研究现状.目前,采用脉冲微孔喷射技术已成功制备出金属、半导体及生体材料单分散微粒子,具有粒径均一、圆球度高等优势.通过与其他微米级粒子制备技术,如均匀液滴喷射法、气动式按需喷射法及雾化法相比较,在诸多方面显示出脉冲微孔喷射法的独特优点.与此同时,分别讨论了脉冲微孔喷射技术在增材制造方面的潜在应用,可直接使用微米级粒子作为增材制造用粉体以及液滴沉积成型.鉴于脉冲微孔喷射技术的独特性,可以预见随着研究的不断深入,脉冲微孔喷射技术将在增材制造方面具有更加广阔的发展空间和应用前景. 相似文献